The meeting on Friday and Saturday in Charlevoix, Quebec, will be the first chance G7 leaders have had to confront President Donald Trump in person since US tariffs on steel and aluminum imports from Canada, Mexico and the European Union were imposed last week.
European leaders criticize the US decision to impose protectionist tariffs on steel and aluminum and to exit the Iran nuclear deal and the Paris climate agreement.
The comments coincide with other claims in a report by the Washington Post, which claims that Trump has hit out at May's "political correctness" in private, stating that May is too anxious about offending other people.
Macron and Trudeau are presenting a united front ahead of the G7, with the French president tweeting of his country's "convergence" with Canada on Wednesday.
Trudeau met with the presidents of the European Council and Commission, Donald Tusk and Jean-Claude Juncker, on Thursday to discuss the EU-Canada trade relationship and discuss "how we can continue to work together to create economic growth that benefits everyone", in what could be seen as a jab at Trump.
"Because these six represent values, represent an economic market, and more than anything, represent a real force at the worldwide level today".
"Please tell Prime Minister Trudeau and President Macron that they are charging the United States massive tariffs and create non-monetary barriers".
According to CNN, when Trudeau pressed Trump to explain how he could use national security as the justification for the tariffs on Canada, the president reportedly replied: "Didn't you guys burn down the White House?"More news: The Other China Challenge
"We will also obviously have some very robust discussions on trade", Trudeau said.
Canada's Trade Minister Francois Philippe Champagne was even more blunt, declaring: "What we are seeing is that the world economic order is under pressure, under attack". Macron, who appeared to have built a warm relationship, said the "G6" leaders would not spark a fight at the summit.
"Because these six countries represent values, they represent an economic market which has the weight of history behind it and which is now a true worldwide force", added Macron after he had his one-to-one with Trudeau earlier in the day. The other six countries signed a sharp condemnation of the president's tariffs earlier this week.
Last week, Trump made a decision to end those exemptions, and the tariffs went into effect on June 1. "So I don't think there's any issue there at all".
The "American president" doesn't seem to "mind being isolated", Macron tweeted Thursday.
The U.S. president has ramped up his criticism of U.S. trading partners, particularly Canada, and demanded major concessions from Canada as well as Mexico in the slow-moving talks to update the North American Free Trade Agreement.
"One risk is that others will take advantage of this apparent vacuum in American leadership and the lack of trans-Atlantic consensus and act in ways that will harm trans-Atlantic interests, whether it's Russian Federation in the Eurasia. or China in Asia", said Ian Lesser, of the German Marshall Fund.